Cooling Fan Velocity Control Apparatus Using Timer and Temperature Sensor

ABSTRACT

An apparatus and method for controlling a velocity of a cooling fan using a timer and a temperature sensor in a set-top box (STB) are provided. An apparatus for controlling a velocity of a cooling fan in an STB may include a temperature sensor unit to change a resistor to be in inverse proportion to an internal temperature, using a thermistor, a timer unit to generate a pulse signal using a capacitor and the resistor of the temperature sensor unit, a switching unit to turn on/off applied voltage, using the generated pulse signal, and a power source unit to apply the voltage to the switching unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2012-0106836, filed on Sep. 26, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an apparatus and method for controlling a velocity of a cooling fan using a timer and a temperature sensor in a set-top box (STB).

2. Description of the Related Art

In most cases, set-top boxes (STBs) are basically operated at all times. Heat may be frequently generated in STBs, which may cause fire hazards. Accordingly, to cool heat generated within an STB during an operation of the STB, a fan, namely a cooling fan, may be attached, and a rotative velocity of the cooling fan may be controlled to prevent performance from being reduced due to heat generation and to maximize the performance.

However, in current STBs, a method of actively controlling a velocity of a cooling fan based on an increase in a temperature is not provided. Typically, a pulse width modulation (PWM) signal is generated by a central processing unit (CPU) or a microcontroller, and a velocity of a cooling fan is controlled. The above method has a limitation on controlling of a velocity of a cooling fan in response to an increase in an internal temperature of a product.

Additionally, when a cooling fan is set to rotate at a high velocity using a currently provided fan velocity control method, a level of generated noise may increase, as a rotative velocity increases.

Accordingly, there is a need for a cooling fan velocity control apparatus that may prevent performance from being degraded due to heat generation, and may reduce generated noise, by actively controlling a velocity of a cooling fan.

SUMMARY

An aspect of the present invention is to provide an apparatus that may actively control a velocity of a cooling fan based on a degree of heat generation. Accordingly, when a cooling fan needs to be used due to heat generated in a central processing unit (CPU) that does not have a function of a temperature sensor, an NE555 timer, and a negative resistance of a temperature sensor, namely a thermistor may be utilized.

Additionally, another aspect of the present invention is to reduce noise generated when the cooling fan is operated, by systematically controlling the velocity of the cooling fan using an on/off state of a timer and by controlling an on/off time of the timer, when a temperature rises.

According to an aspect of the present invention, there is provided a cooling fan velocity control apparatus in a set-top box (STB), including: a temperature sensor unit to change a resistance to be in inverse proportion to an internal temperature, using a thermistor; a timer unit to generate a pulse signal using a capacitor and the resistance of the temperature sensor unit; a switching unit to turn on/off applied voltage, using the generated pulse signal; and a power source unit to apply the voltage to the switching unit.

The timer unit may adjust, using an NE555 timer, a frequency of the generated pulse signal by changing a time constant value of the NE555 timer based on a change in the resistance of the temperature sensor unit, and a frequency output from the timer unit may be obtained by the following equation:

$f = \frac{1.49}{\left( {R_{A} + {2R_{B}}} \right)C_{A}}$

where R_(A) denotes a resistance connected to the timer unit, R_(B) decodes a resistance of the temperature sensor unit, and C_(A) denotes a value of a capacitor connected to the timer unit, and a device value used to adjust the time constant value of the NE555 timer.

As the frequency of the generated pulse signal increases, an on/off switching speed of the switching unit may increase. As the frequency of the generated pulse signal decreases, the on/off switching speed of the switching unit may decrease.

The switching unit may include a transistor. The switching unit may reverse the generated pulse signal and may turn on/off the voltage applied by the power source unit. When a high pulse signal is received, the switching unit may allow the voltage to be applied. When a low pulse signal is received, the switching unit may disallow the voltage to be applied.

The transistor may include an NPN transistor and a positive-channel metal-oxide-semiconductor (PMOS) transistor. The transistor may apply the generated pulse signal to a base of the NPN transistor, and may turn on/off voltage applied to a gate of the PMOS transistor through a collector of the NPN transistor.

EFFECT

According to embodiments of the present invention, there may be provided an apparatus that may actively control a velocity of a cooling fan based on a degree of heat generation, by using an NE555 timer, and a negative resistance of a temperature sensor, namely a thermistor, when the cooling fan needs to be used due to heat generated in a central processing unit (CPU) that does not have a function of a temperature sensor.

Additionally, according to embodiments of the present invention, it is possible to improve a function of reducing noise of a cooling fan by actively controlling a velocity of the cooling fan based on a temperature, when the cooling fan is used to reduce heat generated in a product in a CPU that does not have a function of a temperature sensor. In addition, it is possible to reduce costs, since a separate external microcontroller is not required.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a block diagram to explain a relationship between a cooling fan and a cooling fan velocity control apparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram illustrating a configuration of a cooling fan velocity control apparatus according to an embodiment of the present invention;

FIG. 3 is a circuit diagram illustrating a cooling fan velocity control apparatus according to an embodiment of the present invention; and

FIG. 4 is a diagram illustrating a pulse signal switched by a switching unit and an on/off state of voltage according to an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures.

Hereinafter, a cooling fan velocity control apparatus will be described in detail with reference to the accompanying drawings.

In a current set-top box (STB), an apparatus for actively controlling a velocity of a cooling fan based on an increase in an internal temperature is not provided. Typically, a microcontroller or a central processing unit (CPU) that has a function of a temperature sensor may perform pulse width modulation (PWM) on an internal signal, and may control a cooling fan. However, when a cooling fan needs to be used due to heating of a CPU that does not have the function of the temperature sensor, controlling of the velocity of the cooling fan based on an increase in an internal temperature of a product may be limited.

Accordingly, when a temperature rises, an on/off time of a timer may be adjusted by using an NE555 timer and a negative resistance of a temperature sensor, namely a thermistor. Thus, the velocity of the cooling fan may be systematically may be controlled, and noise of the cooling fan may be reduced.

FIG. 1 is a block diagram illustrating an example in which a cooling fan 120 may be controlled by a cooling fan velocity control apparatus 110 according to embodiments of the present invention. The cooling fan velocity control apparatus 110 may control a rotative velocity of the cooling fan 120, by acquiring information on an internal temperature of an STB, and information on a degree of heating of an internal device, such as a CPU and the like.

The cooling fan velocity control apparatus 110 and the cooling fan 120 may be connected physically or wirelessly. The cooling fan velocity control apparatus 110 may control the cooling fan 120 by acquiring information in real time. A signal to control the cooling fan 120 may be transferred as a digital signal, and the cooling fan 120 may determine a magnitude or code of the transferred signal.

The cooling fan velocity control apparatus 110 may form a circuit including an NE555 timer and a thermistor, to systematically control a velocity of the cooling fan 120 and to adjust a level of noise generated when the cooling fan 120 is operated.

A configuration of the cooling fan velocity control apparatus 110 of FIG. 1 may correspond to a cooling fan velocity control apparatus 200 of FIG. 2, and components of the cooling fan velocity control apparatus 110 may be systematically configured. The cooling fan velocity control apparatus 200 may include a temperature sensor unit 210, a timer unit 220, a switching unit 230, and a power source unit 240.

The temperature sensor unit 210 may include a temperature sensor for a circuit that has a conductivity sensitive to a change in an ambient temperature. The temperature sensor may include, for example, a thermistor, and a resistance characteristic of the thermistor may be changed based on the ambient temperature.

TABLE 1 Temperature (° C.) 10 25 30 40 50 60 70 80 90 100 Resistance 17.8 10 8.3 5.8 4.2 3.1 2.3 1.7 1.4 1 (KΩ)

As shown in Table 1, a thermistor according to the present invention may have a characteristic of a negative resistance temperature coefficient, unlike typical metals. The characteristic of the negative resistance temperature coefficient may indicate that a value of an internal resistance of the thermistor is reduced, as a temperature rises, and the value of the internal resistance is increased, as the temperature falls. In the present invention, the thermistor may function as an input resistor of the timer unit 220 connected to the temperature sensor unit 210, to change a pulse signal generated by the timer unit 220.

The timer unit 220 may output, using a NE555 timer, a signal with a frequency, and may control a velocity of a cooling fan, based on the output signal. The NE555 timer may be used as a stable controller, to generate an exact delay time and a pulse signal. For example, when the NE555 timer is operated as an oscillation device, the NE555 timer may be controlled to obtain an exact pulse signal. A frequency of a signal output through the NE555 timer may be obtained by the following Equation 1:

$\begin{matrix} {f = \frac{1.49}{\left( {R_{A} + {2R_{B}}} \right)C_{A}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \end{matrix}$

As shown in Equation 1, the NE555 timer may receive, as inputs, two resistors and a capacitor, and may generate a frequency. In Equation 1, R_(A) denotes a value of a resistance connected to the timer unit 220, R_(B) decodes a value of a resistance of a thermistor of the temperature sensor unit 210 connected to the timer unit 220, and C_(A) denotes a value of a capacitor connected to the timer unit 220. The above three variables may be used as device values to adjust a time constant of the NE555 timer.

For example, when R_(A) and C_(A) are set to 30 KΩ and 1 uF, respectively, and when a room temperature is set to 25° C., R_(B) may be 10 KΩ, and a frequency of an output signal based on a temperature may be shown as in Table 2.

TABLE 2 Temperature (° C.) 10 25 30 40 50 60 70 80 90 100 Frequency (Hz) 22.7 29.8 31.9 35.8 38.8 41.1 43 44.6 45.4 46.56

As shown in Table 2, a signal with a frequency of 22.7 Hz to 46.56 Hz may be output based on a change in a temperature. Additionally, when R_(A), R_(B) and C_(A) are changed, a cooling fan may be implemented at various velocities.

The switching unit 230 may turn on/off applied voltage using the signal output from the timer unit 220, and may adjust an operation velocity of the cooling fan. Specifically, a signal input to the switching unit 230 may be a digital signal, and a high signal and a low signal may be alternately represented. The high signal and the low signal may be switched and may be output from the switching unit 230. For example, when a high signal is input to the switching unit 230, a low signal may be output from the switching unit 230. Additionally, when a low signal is input to the switching unit 230, a high signal may be output from the switching unit 230.

Based on the signal output from the timer unit 220, the switching unit 230 may turn on or off the applied voltage. For example, when a high signal is received, the switching unit 230 may turn on the applied voltage, that is, may allow the applied voltage. Conversely, when a low signal is received, the switching unit 230 may turn off the applied voltage, that is, may disallow the applied voltage. The voltage may be generated by the power source unit 240, and may be applied to the switching unit 230.

As the frequency of the signal increases, a state of the signal may be quickly switched, that is, a speed of an on/off switching operation may increase. Additionally, as the frequency decreases, the on/off switching operation may be slowly performed. The on/off switching operation may be enabled to be slowly performed using the above operation of the cooling fan, and accordingly it is possible to prevent noise from being generated in an STB.

FIG. 3 illustrates an example in which a cooling fan is connected to a circuit of a cooling fan velocity control apparatus according to embodiments of the present invention. Components of the circuit of FIG. 3 may correspond to components of the cooling fan velocity control apparatus 200, respectively, and may be systematically connected.

In FIG. 3, a temperature sensor unit 310 may be represented as a single resistance, that is, a resistance of a thermistor that may be changed based on an ambient temperature. When a temperature rises, a value of an internal resistance of the thermistor, and a value of resistance R_(B) in the temperature sensor unit 310 may be reduced. When the temperature falls, the value of the internal resistance may be increased, and a frequency of a pulse signal generated by a timer unit 320 may be changed.

The timer unit 320 may include an NE555 timer. The NE555 timer may generate an exact pulse signal through a capacitor and resistor connected to the outside, as shown in FIG. 3. One of two resistors connected to each other may have a negative resistance value of a thermistor of the temperature sensor unit 310, and a design may be performed by adjusting a capacity of a capacitor and other resistance values based on a desired frequency range. Accordingly, the timer unit 320 may output, to a switching unit 330, a signal used to adjust a velocity of a cooling fan 350.

Referring to FIG. 4, a signal input to the switching unit 330 may be switched. In FIG. 4, a signal 410 represents a signal input to the switching unit 330, and a signal 420 represents a signal that is output from the switching unit 330 and that is used to control the cooling fan 350.

The switching unit 330 may include an NPN transistor, and a positive-channel metal-oxide-semiconductor (PMOS) transistor. For example, a pulse signal output from the NE555 timer of the timer unit 320 may be applied to a base terminal of the NPN transistor of the switching unit 330. In this example, when a high pulse signal is output from the timer unit 320, a low pulse signal may be detected in a collector of the NPN transistor. Due to a low pulse signal applied to a gate terminal of the PMOS transistor, voltage applied to the PMOS transistor may be turned off. In FIG. 3, voltage of 12 V may be applied to the PMOS transistor by a power source unit 340.

Conversely, a low pulse signal may be output from the timer unit 320 to the base terminal of the NPN transistor, and a high pulse signal may be output from the collector of the NPN transistor. Accordingly, the high pulse signal may be applied to the gate terminal of the PMOS transistor, and the voltage of 12 V applied to the PMOS transistor by the power source unit 340 may be turned on.

The cooling fan 350 may require power before performing an operation. For example, when a high signal is input to the switching unit 330, a low signal may be output, and may be turned off during the operation of the cooling fan 350. Conversely, when a low signal is input to the switching unit 330, a high signal may be output, and may be turned on during the operation of the cooling fan 350.

Additionally, as a frequency of a signal generated by the timer unit 320 increases, an on/off switching operation may be quickly performed, and accordingly a power switching speed may be increased. As the frequency decreases, the on/off switching operation may be slowly performed, and accordingly noise may be reduced by adjusting driving voltage of the cooling fan 350. In addition, when R_(A), R_(B) and C_(A) of the temperature sensor unit 310 are changed, the cooling fan 350 may be implemented at various velocities.

As described above, a cooling fan velocity control apparatus may actively control a velocity of a cooling fan based on a temperature, and may reduce noise generated in the cooling fan, without a separate microcontroller, when the cooling fan is used to reduce an amount of heat generated in an STB employing a microcontroller or CPU that does not have a function of a temperature sensor.

Although a cooling fan velocity control apparatus according to a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents. 

What is claimed is:
 1. A cooling fan velocity control apparatus in a set-top box (STB), the cooling fan velocity control apparatus comprising: a temperature sensor unit to change a resistance value of a resistor to be in inverse proportion to an internal temperature, using a thermistor; a timer unit to generate a pulse signal using a capacitor and the resistance value of a resistor of the temperature sensor unit; a switching unit to turn on/off applied voltage, using the generated pulse signal; and a power source unit to apply the voltage to the switching unit.
 2. The cooling fan velocity control apparatus of claim 1, wherein the timer unit adjusts, using an NE555 timer, a frequency of the generated pulse signal by changing a time constant value of the NE555 timer based on a change in the resistance value of a resistor of the temperature sensor unit, and wherein a frequency of a signal output from the timer unit is obtained by the following equation: $f = \frac{1.49}{\left( {R_{A} + {2R_{B}}} \right)C_{A}}$ where R_(A) denotes a resistance value of a resistor connected to the timer unit, R_(B) decodes a resistance value of a resistor of the temperature sensor unit, and C_(A) denotes a value of a capacitor connected to the timer unit.
 3. The cooling fan velocity control apparatus of claim 2, wherein, as the frequency of the generated pulse signal increases, an on/off switching speed of the switching unit increases, and wherein, as the frequency of the generated pulse signal decreases, the on/off switching speed of the switching unit decreases.
 4. The cooling fan velocity control apparatus of claim 1, wherein the switching unit comprises a transistor, wherein the switching unit switches a state of the generated pulse signal, and turns on/off the voltage applied by the power source unit, wherein, when a high pulse signal is received, the switching unit allows the applied voltage, and wherein, when a low pulse signal is received, the switching unit disallows the applied voltage.
 5. The cooling fan velocity control apparatus of claim 4, wherein the transistor comprises an NPN transistor and a positive-channel metal-oxide-semiconductor (PMOS) transistor, and wherein the transistor applies the generated pulse signal to a base terminal of the NPN transistor, and turns on/off voltage applied to a gate terminal of the PMOS transistor through a collector of the NPN transistor. 